Before the event: "Who are you going (to the movies) with?". If you were to contact the friend while they were at the movies: "Who are you with?" or "Who's with you?".
EXAMPLE: (Phone conversation) "Yeah, I'm at the baseball game right now."
"Really? Who are you with?"
"Scott and Chuck from the office. We came here straight after work."
I am not sure there is much difference between
1. A is with B and
2. B is with A
I am trying to think of a "theme and rheme" distinction, but really I suspect I would be making it up!
The point about precedence may be more clear if we talk about agreement.
It's a commonplace of negotiating tactics that you should say I agree with you rather than Then you agree with me. The second is much more combative, though they are both saying that you and I are in agreement..